Apparatus and method to hide transit only multi-access networks in OSPF

ABSTRACT

In one embodiment, a Link State Advertisement (LSA) is received from a first router in a network at a second router in the network. The LSA advertises an address of an interface of the first router. The second router determines whether the LSA includes a transit-only identification that indicates the interface of the first router is a transit-only interface. If the LSA does not include a transit-only identification, the second router installs the advertised address of the interface of the first router in a Router Information Base (RIB) of the second router. If the LSA does include a transit-only identification, the second router declines to install the advertised address of the interface of the first router in the RIB of the second router.

RELATED APPLICATIONS

This Application for United States Patent is a continuation of U. S. patent application Ser. No. 11/537,275, now issued as U.S. Pat. No. 7,929,524, filed on Sep. 29, 2006 by Yang et al., and entitled “Apparatus and Method to Hide Transit Only Multi-Access Networks in OSPF”, the contents of which are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

This invention relates to routers. More particularly, this invention relates to routers that are only connected to other routers in a network. Still more particularly, this invention relates to a method for protecting interfaces on these routers from the network to increase security of the network.

BACKGROUND

In today's home and business environment there are many different types of digital networks that allow processing systems to communicate and transmit data between one another. As the size of these networks increases, more routers or other switching systems are needed in the network to transmit data between processing systems. Some systems are so large that some routers have interfaces that are connected directly to other routers to transmit data over the other routers to other systems.

One method for determining a path for transmitting data from one processing system over the network to another system is Open Shortest Path First (OSPF). In OSPF, a router receives Link State Advertisements (LSA) from other routing systems. Each LSA indicates a connection of a router to another system or router. A router then stores the received LSAs and uses the LSAs to determine the path over which to transmit data to a particular address. In the larger networks, the connections between routers are used to transmit data. However, the addresses of the interfaces that connect a router to another router are not needed. Thus, transmitting LSAs with the addresses of these interfaces is a problem. The addresses of the interfaces are installed in Router Information Base (RIB) of other routers when received in an LSA. This wastes router resources as the addresses are stored in the RIB and then the router advertises the link.

Another problem with advertising the addresses for these interfaces is that an attacker can launch an attack on the network by sending packets to one of these interfaces. Thus, there is a need in the art for a system to hide these interfaces from the network to improve convergence of the network and to increase security.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of this invention are described in the following detailed description and are shown in the following drawings:

FIG. 1 illustrating an exemplary network having transit-only routers operating in accordance with this invention;

FIG. 2 illustrating a block diagram of components of a routing system operating in accordance with this invention;

FIG. 3 illustrating a flow diagram of an exemplary process for generating and transmitting a link state advertisement in accordance with this invention; and

FIG. 4 illustrating a flow diagram of an exemplary process for receiving and handling a link state advertisement generated in accordance with this invention.

DETAILED DESCRIPTION

This invention relates to a method to hide transit-only interfaces in a network. For purposes of this discussion, transit-only interfaces are interfaces which directly connect one router to another router. In accordance with the present invention, the routers perform applications which hide the transit-only interfaces in a network in accordance with this invention. These applications may be performed as software, hardware, and/or firmware that are included in the router.

FIG. 1 illustrates a network that includes routing systems that have transit-only interfaces in accordance with this invention. Network 100 includes routing systems 105-111. Routing systems 105-111 are routers, switches, or other processing devices that transmit data to other systems over networks 100. One skilled in the art will recognize that network 100 is shown for illustrative purposes only and the exact configuration of a network is not important to implementing this invention. Thus, the exact configuration and size of a network implementing processes in accordance with this invention are left to one skilled in the art designing a system implementing processes in accordance with this invention. Furthermore, the connection and interfaces of the routing systems shown are for exemplary purposes. The exact number of interfaces and the connections to the interfaces are left to those skilled in the art.

The routing systems in network 100 use OSPF to determine a path for transmitting a packet from one processing system to another. In the exemplary embodiment shown, OSPFv2 is used to make determinations of the paths for transmission of packets. In OSPFv2, Internet Protocol (IP) version 4 (IPv4) addressing is used. Although discussed in terms OSPFv2 and IPv4, one skilled in the art will recognize that this invention may be implemented in other protocols using other addressing strategies.

In network 100, routing systems 105, 106, 110, and 111 connect servers 120-123 to network 100. Routing system 105 connects to server 120 via interface 130 and connects to other routers 106-108 via interfaces 131-133. Routing system 106 connects to server 121 via interface 140 and interfaces 141-143 connect routing system 106 to other routing systems. Routing system 110 connects to server 122 via interface 155 and to other routing systems via interfaces 151-153. Routing system 111 connects to server 123 via interface 145 and to other routing systems via interfaces 161-163.

In network 100, routing systems 107-109 are transit-only routing systems. Routing systems 107-109 are transit-only routing systems because these routing systems are only connected to other routing systems to transmit data between the routing systems that connect processing systems to the network. For example, interface 150 in routing system 108 connects routing system 108 to an interface 160 of routing systems 107.

Routing systems may only have one or a portion of the interfaces in the router that are transit-only. For example, routing system 105 has an interface 133 that connects routing system 105 to routing system 106 via interface 143. Thus, a system for hiding transit-only interfaces may be implemented in all routing systems in network 100.

FIG. 2 shows a router 200. Routing systems 105-111 (Shown in FIG. 1) are all examples of router 200. Router 200 is a routing and/or switching system that transmits digital data, in the form of packets between processing systems connected to a network. One skilled in the art will recognize that router 200 may be a router, switch or any other processing system that receives and transmits digital data.

Router 200 includes ports 205-209. Ports 205-209 connect router 200 to other processing systems in a network. The other processing systems that may be connected include computers, other routers or any other digital processing system. One skilled in the art will further recognize that ports 205-209 are shown for exemplary purposes only and the exact number and configuration of the ports are left to one skilled in the art designing a specific router.

Ports 205-209 are connected to switch circuitry 215. Switch circuitry 215 is circuitry that transmits received packets to the proper ports for delivery to the proper address. One skilled in the art will recognize that there are many different types of circuitry that may be used to transmit packets between proper ports and an explanation of the switching circuitry is not critical to this invention and is omitted for brevity.

Processing unit 220 is connected to switching circuitry 215. Processing unit 220 is a processor, microprocessor, or any combination of processors and microprocessors that execute instructions to perform applications for performing functions in router 200. Processing unit 220 is also connected to a volatile memory 225 and a non-volatile memory 230 via memory bus 235.

Volatile memory 225 is a memory such as a Random Access Memory (RAM). A volatile memory stores instructions and data used by processing unit 220 to perform applications. One such application is a routing operating system. The routing operating system is an application or applications which allow router 200 to perform other applications that provide the functions of router 200. An example of a routing operating system is Inter-network Operating System (IOS) designed by Cisco Systems Inc. One Skilled in the art will recognize that many different types of memory may be used a non-volatile memory such SRAM and DRAM.

Non-volatile memory 230 is a memory such as a Read Only Memory (ROM). Non-volatile memory 230 stores configuration and other vital information for router 200. One skilled in the art will recognize that there are many different types of memory that may be used as a non-volatile memory.

Modules 240, 245, and 250 are connected to switching circuitry 215. Modules 240, 245, and 250 are devices and/or software that prepare specific features in router 200. An example of a module is a Voice Over Internet Protocol (VoIP) module for providing telephonic communications to processing devices connected to router 200. One skilled in the art will recognize that the number of modules and the functions that each module provides may be determined by one skilled in the art designing a particular router.

In accordance with this invention, a system for hiding transit-only interfaces of routing systems is provided by processes executed by the routing systems as shown by the following exemplary embodiments. One skilled in the art will recognize that the following processes may be executed by software, firmware, hardware, and/or any combination of the preceding components.

In order to hide transit-only interfaces, a routing system must be able to identify a transit-only interface to other routing systems and the other routing systems must know how to handle an interface that is identified as transit only. FIG. 3 illustrates an exemplary embodiment of a process executed by a first routing system to identify transit-only interface in advertisements. FIG. 4 then illustrates an exemplary embodiment of a process for a router receiving an advertisement of a transit-only interface and storing the information.

FIG. 3 illustrates an exemplary process 300 executed by a routing system to identify a transit-only interface to other routing systems. Process 300 begins in step 305 by the routing system determining that an interface is a transit-only interface. The determination is performed in a typical manner that a routing system performs detections of connections to the routing system. If the interface is determined not to be a transit-only interface, the routing system generates an advertisement in a normal manner in accordance with the art in step 310. One skilled in the art will recognize that the advertisement is an LSA in OSPF and is generated in the manner defined in OSPF. The advertisement is then transmitted in the normal manner in step 325.

If the interface is determined to be transit only, an advertisement is generated in step 315. In the preferred embodiment, the advertisement is an LSA and is generated in a typical manner. After the advertisement is generated, a transit-only identification is inserted into the packet to indicate that the advertised interface is transit-only in step 320.

In exemplary embodiments, there are a variety of manners in which an advertisement for a transit-only interface may be marked. A first method for marking a transit-only interface is by placing an invalidate and/or non-continuous network mask instead of the configured value for the network. For example, the value 0x00000001 may be inserted instead of the configured value. Because the network mask is invalid the OSPF does not install the address in the RIB. In a network using this method, some vendors may do a sanity check and when the advertisements with invalid masks are detected, these advertisements may be dropped. This could disrupt communications over the network.

A second method for marking advertisements for transit only interfaces uses a valid, designated network mask, such as, a network mask that should not be used in a multi-access network. Some examples of this include 0xffffffff and 0xfffffffe. Routing systems using a system in accordance with the invention must not place the advertised addresses in the RIB. However, non-upgrades systems will still flood the networks with the advertisements. Thus, this method is more predictable than using an invalid mask. However, the host addresses of a transmitting routing system may be installed in the RIBs of non-upgraded systems. Thus, the interfaces may still be attacked.

A third method for marking advertisements for transit-only interfaces is to place a flag or administrative tag in the advertisements. Such tags are described in the IETF draft of “Extensions to OSPFv2 for advertising Optional Rout/Link Attributes.” This will require all routers to be upgraded to read the tag and recognize the advertisement is for a transit-only interface. Furthermore, this method requires support of opaque Link State Advertisements. This may cause backward compatibility issues.

After the advertisement is generated and the mask is inserted, the advertisement is transmitted in the conventional manner in step 325. In step 330, the router determines whether all of the advertisements for interfaces have been transmitted. If there are more advertisements to generate, process 300 repeats for step 305. Otherwise process 300 ends.

FIG. 4 illustrates an exemplary process executed by a routing system when an advertisement is received to hide a transit-only interface in accordance with this invention. Process 400 begins in step 405 with an advertisement being received by the routing system. In step 410, the identifier is read.

The routing system then determines whether the advertised address is a transit-only interface in step 415. If the first method of using an invalid mask is used, all routing systems will recognize the invalid mask and not install the address in the RIB. If the second or third methods are used, the receiving routing systems must be upgraded to detect the identifier. If the identifier is read from the advertisement, the advertisement information is stored in a conventional manner. However, the advertised address is not stored in RIB of the routing system in step 420. If the identifier is not read, the advertised information is stored in the conventional manner in step 425. Process 400 then ends.

The above is a description of exemplary embodiments of a method for hiding transit-only interfaces in a network. It is envisioned that those skilled in the art can and will design alternative systems for hiding transit-only interfaces that infringe on this invention as set forth in the following claims either literally or through Doctrine of Equivalents. 

What is claimed is:
 1. A method comprising: receiving a Link State Advertisement (LSA) from a first router in a network at a second router in the network, the LSA advertising an address of an interface of the first router; determining whether the LSA includes a transit-only identification that indicates the interface of the first router is a transit-only interface, wherein a transit-only interface is an interface that directly connects to only interfaces of one or more other routers to transmit data from router to router; if the LSA does not include a transit-only identification that indicates the interface of the first router is a transit-only interface, installing the advertised address of the interface of the first router in a Routing Information Base (RIB) of the second router; and if the LSA does include a transit-only identification that indicates the interface of the first router is a transit-only interface, declining to install the advertised address of the interface of the first router in the RIB of the second router.
 2. The method of claim 1, wherein the LSA is an Open Shortest Path First (OSPF) LSA.
 3. The method of claim 1, further comprising: determining, by the first router, whether the interface of the first router is a transit-only interface; generating the LSA; and if the interface of the first router is a transit-only interface, inserting the transit-only identification in the LSA.
 4. The method of claim 1, wherein the transit-only identification is a network mask.
 5. The method of claim 4, wherein the network mask is 0xffffffff.
 6. The method of claim 4, wherein the network mask is 0xfffffffe.
 7. The method of claim 4, wherein the network mask is 0x00000001.
 8. An apparatus comprising: an interface; a memory configured to maintain a Routing Information Base (RIB); and a processing unit configured to execute a process to upon receipt of a Link State Advertisement (LSA) from a first router that advertises an address of an interface of the first router, determine whether the LSA includes a transit-only identification that indicates the interface of the first router is a transit-only interface, in response to the interface of the first router not being indicated to be a transit-only interface, install the advertised address of the interface of the first router in the RIB, and in response to the interface of the first router being indicated to be a transit-only interface, decline to install the advertised address of the interface of the first router in the RIB.
 9. The apparatus of claim 8, wherein the LSA is an Open Shortest Path First (OSPF) LSA.
 10. The apparatus of claim 8, wherein the transit-only identification is a network mask.
 11. The apparatus of claim 10, wherein the network mask is 0xffffffff.
 12. The apparatus of claim 10, wherein the network mask is 0xfffffffe.
 13. The apparatus of claim 10, wherein the network mask is 0x00000001.
 14. An apparatus comprising: means for receiving a Link State Advertisement (LSA) from a first router, the LSA advertising an address of an interface of the first router; means for determining whether the LSA includes a transit-only identification that indicates the interface of the first router is a transit-only interface, wherein a transit-only interface is an interface that directly connects to only interfaces of one or more other routers to transmit data from router to router; means for installing the advertised address of the interface of the first router in a Routing Information Base (RIB) of the second router, in response to the LSA not including a transit-only identification that indicates the interface of the first router is a transit-only interface; and means for declining to install the advertised address of the interface of the first router in the RIB of the second router, in response to the LSA not including a transit-only identification that indicates the interface of the first router is a transit-only interface.
 15. The apparatus of claim 14, wherein the LSA is an Open Shortest Path First (OSPF) LSA.
 16. The apparatus of claim 14, wherein the a transit-only identification is a network mask.
 17. The apparatus of claim 16, wherein the network mask is 0xffffffff.
 18. The apparatus of claim 16, wherein the network mask is 0xfffffffe.
 19. The apparatus of claim 16, wherein the network mask is 0x00000001.
 20. A method comprising: generating a Link State Advertisement (LSA) at a first router, the LSA advertising an address of an interface of the first router; determining whether the interface of the first router is a transit-only interface, wherein a transit-only interface is an interface that directly connects to only interfaces of one or more other routers to transmit data from router to router; in response to determination that the interface of the first router is a transit-only interface, placing an transit-only identification in the LSA that indicates that the advertised address of the interface included in the LSA should not be stored in a routing information base (RIB) of a second router that receives the LSA; in response to determination that the interface of the first router is not a transit-only interface, omitting the transit-only identification; and sending the LSA from the first router to the second router.
 21. A non-transitory computer-readable medium encoded with software thereon, the software when executed by a processor operable to: examine a received advertisement from a first router at a second router, the advertisement advertising an address of an interface of the first router; determine whether the advertisement includes a transit-only identification indicating the interface of the first router is used to transmit data from router to router; in response to absence of the transit-only identification, install the advertised address of the interface of the first router in a Routing Information Base (RIB) of the second router; and in response to presence of the transit-only identification, prevent installation of the advertised address of the interface of the first router in the RIB of the second router.
 22. The non-transitory computer-readable medium of claim 21, wherein the advertisement is a link state advertisement (LSA).
 23. The non-transitory computer-readable medium of claim 21, wherein the software when executed is further operable to: determine the interface of the first router is a transit-only interface; generating the advertisement; and insert the transit-only identification in the advertisement.
 24. The non-transitory computer-readable medium of claim 21, wherein the transit-only identification is a particular network mask.
 25. The non-transitory computer-readable medium of claim 21, wherein the transit-only identification is an administrative tag. 